The present invention relates to a ventricular assist device used for circulatory assistance of a patient suffering from heart failure, methods of controlling the same, and an auxiliary apparatus therefor. More particularly, the present invention relates to a ventricular assist device capable of promoting recovery of the function of the native failing heart, methods of controlling the same, and an auxiliary apparatus therefor.
A ventricular assist device for circulatory assistance, as an example of a ventricular assist device of interest to the present invention, is disclosed in Japanese Patent Laid-Open No. 55-141250. FIG. 11 shows a manner of attachment of the ventricular assist device to the native heart. As shown in FIG. 11, the human heart 30 is composed broadly of the right heart for the pulmonary circulation and the left heart for the systemic circulation. The right heart is divided into the right atrium 31 and the right ventricle 32; the left heart, into the left atrium 33 and left ventricle 34. The blood flows in the following order: the venous blood returning from the systemic circulation enters the right atrium through the superior and inferior venae cavae, and then passes into the right ventricle, whose contraction forces it through pulmonary artery to the lung. There, it is oxygenated by the function of respiration, and next is returned through the pulmonary veins to the left atrium 33. After this, the blood enters the left ventricle 34 and is pumped into the aorta by the contraction of left ventricle 34, and then back to the systemic circulation. Here, a ventricular assist device 37 is used to pump blood from the left atrium 33 or left ventricle 34 into the aorta.
Conventional ventricular assist devices have been used in the above-described manner. The conventional ventricular assist device is in an operational mode such that it sucks blood from the native heart 30 and the ventricular assist device 37 pumps the blood into the artery. This operational mode suggests that the conventional ventricular assist device is mainly designed to functionally substitute for an incompetent native heart 30.
Therefore, the higher the flow rate of the conventional ventricular assist device, the smaller the amount of blood loaded in the ventricle during diastole, thus impairing relaxation and filling of the native heart 30. Furthermore, in most cases, the native heart 30 has to eject some amount of blood into the aorta against the aortic pressure, although the ventricular assist device draws sufficient blood, suggesting that the ejection resistance is too high for the heart with insufficient function. To summarize, the conventional ventricular assist device does not provide the ideal environment for recovery of the function of native heart 30, because it impairs relaxation and filling of native heart 30 and imposes high ventricular load.
Therefore, an object of the present invention is to provide a ventricular assist device capable of promoting recovery of an incompetent native heart.
Another object of the present invention is to provide a ventricular assist device, which is not only capable of promoting the recovery of a failing heart but also available in the case of ineffective contraction of the heart, as seen in ventricular fibrillation.
The other object of the present invention is to provide an auxiliary apparatus, which is capable of promoting the recovery of a failing native heart, for a conventional ventricular assist device.
A ventricular assist device in accordance with the present invention includes a blood conduit that carries blood from the ventricle toward the ventricular assist device, a one-way valve that is provided within the blood conduit and can open only toward the ventricular assist device, an afterload-controlling chamber that temporarily stores the blood ejected through the one-way valve from the ventricle of native heart, pressure-controlling means for maintaining pressure of the afterload-controlling chamber within such a predetermined range that is lower than the arterial pressure and higher than the ventricular diastolic pressure, a blood pump that draws blood from the afterload-controlling chamber and pumps the blood into the artery, a control unit for the blood pump, and a feeding tube.
During ventricular diastole, the pressure of afterload-controlling chamber is maintained at pressure levels that can close the one-way valve, which opens only toward the afterload-controlling chamber. Thereby, the blood pump does not suck the blood from the ventricle, and neither relaxation of the ventricle nor filling is limited. During ventricular systole, the pressure of afterload-controlling chamber is maintained sufficiently lower than the arterial pressure. Therefore, the ventricle is able to eject blood into the afterload-controlling chamber with very low ejection resistance, but not into the artery with much higher ejection resistance. The blood ejected into the afterload-controlling chamber is sucked and fed to the artery by the blood pump that is provided distal to the afterload-controlling chamber. As a result, the ventricle is able to eject blood with a low ejection resistance after sufficient relaxation and filling of the ventricle. Therefore, the functional recovery of native failing heart can be promoted.